There are over 1,300 of them. The largest are located in the Neman River delta. Sinkhole lakes (Lithuanian: karstiniai ežerai) are prevalent in the Biržai district municipality. There are about 300 such lakes, although their surface area covers only 10 hectares. It has been suggested that most of them are interconnected. Underground lakes (Lithuanian: požeminiai ežerai) are also found in the Biržai district municipality. The largest one is in Cow's Cave (Lithuanian: Karvės ola); its water temperature is a constant +4.5 degrees Celsius. A marine lake (Lithuanian: lagūniniai or jūriniai ežerai), Krokų Lanka, was formed when various drifts from the Neman River separated a part of the Curonian Lagoon. It is the only such lake in Lithuania. Reservoirs (Lithuanian: tvenkiniai or kūdros) were created when a river was dammed, or were excavated as a local project. There about 3,400 such lakes, but only 340 of them cover more than 5 hectares. Most of the dams were built during the second part of the 20th century when the Soviet government authorities organized massive land use changes. Largest lakes Other notable lakes Lake Asveja has the longest coastline - almost 30 kilometers, when all its inlets are considered. It is also the third deepest lake (50.2 m). Lake Tauragnas is the deepest (62.5 m) lake in Lithuania and it has the highest altitude above sea (165 m). Lake Baluošas has an island that contains its own tiny lake. Lake Žuvintas is a strictly protected body of water. It is the shallowest lake in Lithuania; its greatest depth is 3 meters, averaging 1 meter. It is a notable waterfowl habitat, but is filling with vegetation. Lake Galvė's island houses Trakai castle. Lithuania's largest lake is Drūkšiai. Its catchment area covers the surrounding creeks, coastal wetlands and forests. The lake is surrounded with many types of rare vegetation not only in Lithuania but also throughout Europe, and the lake itself is valuable as a habitat of rare birds, crustaceans and fish species. Lake Sartai has the longest coastline in Lithuania – as many as 79 km. Also it has a variety of fish: rope, perch, pike, roach, bream, roach, bleak, silver bream, ide, catfish, chub, and other fish. Plateliai is one of the most transparent lakes in Lithuania, its bottom terrain is very diverse, with many depths and shallows. References Stasys Vaitiekūnas, Elena Valančienė, Lietuvos geografija (Geography of Lithuania), 2004, Alma littera, Ežerai (Lakes),